Cryotreatment, a therapy that uses that removal of heat from tissue, is often used to treat cardiac conditions such as cardiac arrhythmias. In most cryotreatment procedures, a pressurized refrigerant is circulated within the tip of a cryotreatment catheter, where the refrigerant expands and absorbs heat from surrounding tissue. As the tissue freezes, blood adjacent the treatment site may also freeze, creating an “ice ball” that temporarily adheres the treatment element (for example, a cryoballoon or thermally conductive area at the tip of the cryotreatment device) to the tissue at the treatment site, a phenomenon called cryoadhesion.
Cryoadhesion is advantageous in that it helps prevent the cryotreatment device from moving away from the target treatment site of a beating heart. However, research has shown that a freeze-thaw-freeze cycle more effectively ablates tissue than a single longer freeze-only cycle. Although more efficient lesion creation is desired, the freeze-thaw-freeze cycle may also result in the thawing of the ice ball that keeps the cryotreatment device in place. As a result, the device must be repositioned, which may be complicated and time-consuming. Further, some cryotreatment procedures, such pulmonary vein isolation (PVI), involve the use of fluoroscopy to visualize the position of the device and to make sure that, for example, the pulmonary vein is completely occluded. Fluoroscopy involves x-ray visualization; consequently, each time the ice ball thaws and the cryotreatment device is repositioned, the patient and the user are exposed to an increased amount of radiation.
In most cryotreatment systems that include an inflatable treatment element such as a cryoballoon, the system includes an inflation reservoir that is used to inflate the cryoballoon. An ablation procedure using systems such as this may require several stages. In the inflation stage, the inflation reservoir is filled with coolant at or near room temperature (that is, at temperatures not low enough to cause tissue ablation), and this volume is then used to inflate the cryoballoon, allowing for device positioning before the cryoballoon reaches ablation temperatures. The system may then enter one or more transition, ablation, evacuation, and refilling stages. Coolant flow may be stopped during the evacuation and refilling stages, and therefore the ice ball may be allowed to thaw and cryoadhesion may be broken.
Such fixed initial volume systems may only be used for a specific device, as the size of the inflation reservoir is predetermined, and cannot be adapted for use with, for example, a different type or size of device or newer generation of a device. If a user wants to substitute a different device, or even if a newer generation of a current device is developed, the entire system may have to be replaced. Additionally, these systems are generally “on/off” and do not easily allow for temperature modification during an ablation procedure.
Therefore, it is desirable to provide a method and system for more efficient cryotreatment, while reducing the need for fluoroscopy. It is also desirable to provide a continuous system that is usable with a variety of devices.